Polymers of the acrylic series possess a whole range of promising properties such as transparency, high mechanical strength, ageing-resistance, emulsifying and coagulating properties and other valuable characteristics. For this reason, demand for these polymers is continuously growing simultaneously with stricter requirements imposed on the quality of these polymers. This gives an impetus for the elaboration of numerous processes for the production of polymers and copolymers of the acrylic series.
Known in the art are methods for obtaining polymers and copolymers of the acrylic series by the reaction of (co)polymerization in bulk, or solutions which are divided into the varnish method in the case where the starting monomers and the resulting (co)polymer are soluble in the solvent, and the suspension method in the case where the monomer and the reaction product are insoluble in the solvent. The suspension method is intermediate relative to the varnish and emulsion methods.
It is also known to produce polymers by way of (co)polymerization of the starting monomers in the solid phase or melt, but these methods of (co)polymerization have not yet found commercial implementation.
The reaction of (co)polymerization in bulk or in aqueous solutions enjoys extensive commercial application. In the majority of cases, the processes are commercially implemented discontinuously and less frequently--continuously. This is due to the multi-stage character of the manufacture of the final product. Thus, the process for the manufacture of such polymeric materials involves the following stages: (co)polymerization, granulation, drying and crushing or (co)polymerization, washing, centrifugation or filtration and, when required, crushing which is performed in the above-indicated sequence.
Polymers of the acrylic series are produced mainly by the suspension method in reactors with thermostatted jackets provided with stirring means. Polymerization is effected at a monomer concentration of 15% in a solution of inflammable and explosive toxic solvents. In these processes 6 tons of organic-containing waste waters are obtained per ton of the final product which necessitates special measures for their utilization. In certain cases the quality of the obtained product does not meet the requirements specified by the customer.
Known is a process for the production of water-soluble powder-like (co)polymers by way of spraying a rubber-like (co)polymer with a concentration above 20% into a medium consisting of water and an organic solvent (cf. Japanese Pat. No. 48-9576, published in 1973). This manner of polymerization of the monomers results in a higher quality of the final product. However, the presence of an organic solvent in the system eventually results in the formation of considerable amounts of organic-containing waste waters and does not improve working conditions for the operating personnel.
Water-soluble (co)polymers based on acrylamide and acrylic acid are produced in the solid state by the emulsion method (cf. British Pat. No. 1,319,632 published 1973). The process of (co)polymerization of aqueous solutions of the monomers is carried out in a water-oil emulsion in the presence of an organic hydrophobic liquid forming an azeotropic mixture with water. The final stage of the process is the removal of water from the product by way of azeotropic distillation. The presence of residual water in the product, as well as the use of the water-oil emulsion and organic liquid causes contamination of the end product with these components, thus substantially lowering the process efficiency.
Polymers of methacrylic acid esters are produced in a film-type reactor provided with a stirring means, wherein the reaction occurs in a film flowing down along the reactor walls (cf. Japanese Pat. No. 47-16173 published 1972). This process being highly effective, however, makes it possible to obtain the products only in the liquid state. In the treatment of high-viscosity solutions which adhere to the apparatus walls, difficulties associated with agitation of the reaction medium occur.
Copolymers comprising water-soluble macromolecular acrylic gels are produced in a vertical cylindrical polymerizer with its inner surface coated by a resin to facilitate the removal of the product (cf. Japanese Pat. No. 49-36954, published 1974). The process steps are carried out in the following sequence. The starting components are charged into a polymerizer and a heating agent is fed into the jacket to control the polymerization temperature. The copolymerized mass is discharged through the opened lower bottom of the polymerizer. The rubber-like product is further subjected to granulation and drying. In this process, it is impossible to use high concentrations of the starting monomers, since it results in the formation of a solid product which is difficult to remove from the apparatus. Furthermore, high concentration of the components causes the evolution of great amounts of heat which does not make it possible to use large-diameter apparatus.
Known in the art is a batch-wise process for the production of water-soluble polymers in a cylindrical reactor elongated in the direction of its axis, wherefrom the product is discharged by means of a piston (cf. FRG Pat. No. 1,218,157 published 1971). The reactor operates under substantially adiabatic conditions. In this process only small concentrations (20-40%) of the components can be used. The product comprises a rubber-like mass which is substantially impossible to process by cutting. This mass is then subjected to vacuum drying. The use of high concentrations of the starting monomers is associated with difficulties in moving the polymerizate in the apparatus and removal of the heat liberated in the reaction of copolymerization.
Known is a continuous process for producing a polymer from polymerizable ethylenically unsaturated compounds (cf. British Pat. No. 1,062,980 published 1967). It is carried out in a tubular reactor with forced feeding under a pressure of from 10 to 1,000 atm and at a temperature within the range of from 100.degree. to 300.degree. C. To obtain the product with a uniform molecular mass, the molten polymer is subjected to shear stresses and the volatile components are removed from the polymerized product in the outgassing zone. The process continuity is its advantage. However, the use of high pressures of up to 1,000 atm and further reduction thereof to 1-100 mm Hg is associated with certain difficulties. The product is subject to thermal destruction. Therefore it is obtained at a temperature below the melting point which, in turn, causes difficulties in its movement in the apparatus in the solid state. Using low concentrations of the monomers, it is possible to produce a rubber-like substance, but its disintegration is also associated with certain difficulties and necessitates an additional drying operation.
Known in the art is a continuous process for the production of a water-soluble polymer (cf. French Pat. No. 2,104,041 published 1972). This process is performed in an apparatus comprising a mixer for the starting components, an elongated reactor with drawing rolls mounted in its lower section, a granulator and a belt conveyor blown over with air to prevent granules from clogging. The starting components are fed into the mixer having an impeller of a vane or any other type. After vigorous stirring, the reaction mass is fed into an elongated reactor of round, square or any other cross-section, wherein at 1/3 of the reactor height a zone of intensive polymerization is formed due to the evolving heat of polymerization. In the course of movement of the reaction mass towards the drawing rolls, the polymerization reaction is completed and the product is cooled to ambient temperature.
The product is then drawn by rolls into a granulator, disintegrated and delivered onto a belt conveyor. Therefrom, granules are fed to drying. In this process the product is obtained at low (below 40%) concentrations of the starting monomers. The use of higher concentrations is associated with difficulties in the removal of heat formed in the reaction of polymerization and displacement of the material in the apparatus.
Known in the art is also a process for the production of water-soluble polymers, wherein no organic-containing waste waters are formed. The polymer is obtained by spraying the reaction mixture in the presence of initiators with the boiling point above 100.degree. C. (cf. U.S. Pat. No. 3,644,305 published 1973). In the process, use is made of a reaction mass with a concentration of the starting components of 30% by mass. The product is very soluble in water and the degree of conversion in its manufacture is 99%. However, the product has a low molecular mass.
It follows from the foregoing analysis of the prior art that the known processes for the production of (co)polymers do not make it possible to obtain a product which meets growing customer requirements.